What is Arthrosis (Osteoarthritis)?
Arthrosis, clinically termed osteoarthritis (OA), is a degenerative joint disease characterized by whole-joint pathology including cartilage degradation, bone remodeling, osteophyte formation, and synovial inflammation, leading to pain, stiffness, swelling, and loss of normal joint function. 1
Disease Definition and Scope
Osteoarthritis is the most common form of arthritis worldwide, affecting an estimated 302 million people globally and representing the primary diagnosis for 23.7 million ambulatory care visits in the United States in 2013. 1 Between 2008 and 2014, an estimated 32.5 million adults in the US (14% of the American population) suffered from symptomatic knee osteoarthritis. 1
The American College of Rheumatology defines OA as a "heterogeneous group of conditions that leads to joint symptoms and signs which are associated with defective integrity of articular cartilage, in addition to related changes in the underlying bone at the joint margins." 2
Pathophysiology
OA involves pathology of the entire joint, not just cartilage, including: 1, 3
- Cartilage degradation with progressive loss of proteoglycans and mineralization of the extracellular matrix 4
- Subchondral bone remodeling and osteophyte (bone spur) formation 1, 4
- Synovial inflammation (synovitis) with mild intraarticular inflammation 2, 3
- Hypertrophic differentiation of chondrocytes attempting to recapitulate early developmental phenotypes 3
The disease represents a complex interplay of mechanical, inflammatory, and metabolic pathways that remain incompletely understood in their totality. 4
Clinical Presentation
Patients with OA typically present with joint pain accompanied by functional limitation and reduced quality of life. 1 The cardinal symptoms include: 1, 5
- Joint pain worsened by movement that can lead to disability in activities of daily living 5
- Stiffness, particularly after periods of inactivity 1
- Swelling around affected joints 1
- Loss of normal joint function with progressive disability 1
The knees, hips, and hands are the most commonly affected appendicular joints. 1
Risk Factors
Immutable Risk Factors
According to the American Geriatrics Society, non-modifiable risk factors include: 6, 7
- Age (the single most important constitutional risk factor) 7
- Female gender (women represent 78% of OA diagnoses despite being 51% of the population) 1
- Genetic inheritance (heritability estimates of 39-65% for knee/hand OA, 60% for hip OA, and 70% for spine OA) 6
- Congenital malformations 6
Modifiable Risk Factors
The American Geriatrics Society identifies modifiable factors as: 6, 7
- Obesity (increases risk in both weight-bearing and non-weight-bearing joints through metabolic mechanisms) 7
- Muscle weakness (particularly quadriceps weakness creating a vicious cycle) 7
- Heavy physical activity and repetitive occupational joint loading 7
- Physical inactivity 6
Potentially Modifiable Risk Factors
- Joint trauma (accounts for a significant fraction of OA cases) 7
- Abnormal joint alignment altering load distribution 7
- Reduced proprioception and poor joint biomechanics 6
Epidemiology
Worldwide prevalence of radiographically confirmed symptomatic knee OA is estimated at 3.8% overall, increasing to more than 10% in populations older than 60 years. 1 The prevalence after age 65 years is approximately 60% in men and 70% in women. 2
The incidence of knee OA in the United States is estimated at 240 persons per 100,000 per year. 1 OA is a leading cause of disability among older adults, with affected individuals visiting physicians more frequently and experiencing greater functional limitations than others in the same age group. 1
Disease Course
OA spans decades of a patient's life, requiring long-term management with multiple pharmaceutical and nonpharmaceutical interventions, often in combination. 1 The disease course and patient requirements change over time, necessitating periodic review and readjustment of therapy rather than rigid continuation of a single treatment. 2